It is a well-known that the thermal displacement of a machine tool or a numerical control machine tool is influenced generally by the temperature environment in which the machine tool is installed, for example, the room temperature, the temperature distribution, or the radiant heat applied to the machine tool. The thermal displacement also depends on the heat generated by the machine tool per se such as, for example, heat due to running of a spindle system, a drive system or sliding parts. Other sources of heat may be heat from a hydraulic-pressure generating apparatus serving as a power source for the machine tool, heat of a hydraulic fluid transmitted to the machine tool through piping and hydraulic control instruments, heat generated due to machining or processing, heat of chips or machining oil, heat generated from a driving motor or a control apparatus, or the like.
As a countermeasure to prevent such thermal displacement, a direct compensation system has been proposed in which thermal displacement of a system is estimated. The system is then operated with an integrated power given to a drive system. Position correction is applied to correct for thermal displacement at each .delta.t, as disclosed in Japanese Patent Laid-Open No. SHO 63-256336 entitled "A method of correcting thermal displacement of a ball screw in an NC machine". The periods .delta.t are identical in this conventional embodiment.
Further, other indirect techniques are known. For example, there is a method in which a cooling oil maintained at low temperature is recirculated about a bearing structure for a spindle in order to suppress generated heat of the spindle, a method in which a cooling oil maintained at low temperature flows through a hollow ball screw to maintain the ball screw at predetermined or constant temperature in order to suppress generated heat of a drive system, a method in which a cooling oil maintained at low temperature flows through the inside of a sliding part to maintain the sliding part at predetermined or constant temperature in order to eliminate generated heat of the sliding part, a method in which a cooling oil maintained at low temperature flows through the inside of each structural part of a machine tool in order to cope with temperature distribution within a room, to reduce influence of a difference in the temperature distribution, a method in which temperature of a machining oil is maintained constant, and the like, these methods have already been put into practice in part.
In these methods, however, it is also a well-known fact that equipment and/or installation costs is raised with an increase in the correction accuracy. Further, where the above-described methods are used, it is also a fact that the correction accuracy under changing machining conditions fall short of expectations.
Prior to the present invention, thermal displacement in an existing system has been measured by simulated operation with a machining center serving as a model, according to the following methods and with the following results:
I. Operation No. 1
A. Measuring Method:
(1) The machine used was a vertical machining center having: a semi-closed feed-back control system. PA1 (2) Simulated-running moving axes were X, Y and Z axes, as seen in FIGS. 21(a) and 21(b). PA1 (3) Displacement measuring axes were the X-axis/Y-axis (each of which subject due to an absolute-value measurement by a laser-measuring system) as seen in FIG. 21(a). PA1 (4) A workpiece 102 reference-position measurement was made for X-axis/Y-axis (both using the same first touch probe 101) and for spindle 104 along a Z-axis (using a second touch probe 103) as seen in FIGS. 21(a) and 21(b). PA1 (5) The measurement procedure was executed in accordance with the following steps: First, the vertical machining center, the measuring instruments and the like were left alone in a room whose temperature was 20.degree..+-.0.5.degree. C. for seventy-two (72) hours or more. Secondly, a power source was turned on. Thirdly, returning to the origin was practiced. Fourthly, a workpiece reference position was measured: X, Y and Z. Fifthly, the laser measuring system was set to 0 (zero). Sixthly, the machine was moved to a 0 (zero) point. Seventhly, measurement was executed due to the laser measuring system having an accuracy at which the machine is in the 0 position. Eighthly, a workpiece reference position was measured. Ninthly, measurement was done due to the laser measuring system at a position of a 6-12 drilled bore. Tenthly, simulated running was done, one or five times. Eleventhly, the workpiece reference position was measured. Twelfthly, a position of a 6-12 drilled bore was measured by the laser measuring system. Thirteenthly, the above-described steps 2.about.12 were executed repeatedly. Fourteenthly, an electric power source was turned off. PA1 (6) The simulated running conditions were such that a program was prepared with a workpiece illustrated in FIG. 22 being assumed, and idle-runs were conducted with the workpiece not being mounted. Processing was estimated such that an upper surface was rough-processed with five (5) divisions and was finish-milled, was 6-12 drilled, was 7-8.2 drilled, and was 7-10 thread machining (tapped). PA1 (1) A change or variation of the machine 0-point position accuracy with time was experienced, as illustrated in FIG. 23 (X-Y measurement using a laser measuring system). Specifically, the X-coordinates move gently toward a minus direction through 4 .mu.m substantially without fluctuation and, subsequently, are restored gently until 2.6 .mu.m. Also, the Y-coordinates move gently toward a plus direction through 10.03 .mu.m substantially without fluctuation. PA1 (2) A change in X, Y and Z workpiece reference positions with time was experienced, as illustrated in FIG. 24. Specifically, the X-coordinates generally and steadily change by +12 .mu.m over about eight (8) hours without fluctuation. However, the Y-coordinates experience an initial decrease with a gradual change of +11 .mu.m over about eight (8) hours while the Y-coordinates are fluctuated a little through 3.about.5 .mu.m. Thirdly, Z-coordinates retain a change of -8 .mu.m over about eight (8) hours while the Z-coordinates are fluctuated a little through 1.1.about.2 .mu.m. PA1 (3) A change of a first bore, a fourth bore and a sixth bore of the 6-12 drilled bores is as illustrated in FIG. 25 (measurement is made by the laser measuring system). That is, first, a position of the first bore changes through 2.38 .mu.m in an X-minus direction and, subsequently, is restored to plus 0.47 .mu.m and changes through 6.83 .mu.m in a Y-plus direction. Secondly, a position of the fourth bore changes through 8.22 .mu.m in the X-minus direction and changes through 3.96 .mu.m in the Y-plus direction. Thirdly, a position of the sixth bore changes through 2.22 .mu.m in the X-minus direction and, subsequently, changes to plus 0.63 .mu.m; it also changes through 3.96 .mu.m in the Y-minus direction. PA1 (1) The machine used was a vertical machining center having a semi-closed feed-back control system. PA1 (2) The simulated-running moving axis was the X-axis. PA1 (3) The displacement measuring axis was the X-axis (an absolute-value measurement due to a laser-measuring system). PA1 (4) A workpiece 102 reference-position measurement was made for the X-axis/Y-axis (both using the same touch probe 101) and for the Z-axis (using a second 103 touch probe). Reference can be made to FIGS. 21(a) and 21(b) regarding installation or arrangement conditions. PA1 (5) The measurement procedure was executed in accordance with the following steps: First, the vertical machining center, the measuring instruments and the like were left alone in a room whose temperature was 20.degree..+-.0.5.degree. C. for seventy-two (72) hours or more. Secondly, a power source was turned on. Thirdly, returning to the origin was practiced. Fourthly, a workpiece reference position was measured; X, Y and Z. Fifthly, the laser measuring system was set to 0 (zero). Sixthly, X-axis 10 mm-pitch position accuracy was measured (using laser measuring system). Seventhly, machine 0-point position accuracy was measured using the laser measuring system. Eighthly, simulated running was conducted a) one time of 250* 300 block processing program, b) continuously in accordance with a program of 250*300 block processing, c) continuously in accordance with a program of movement of rapid traverse and cutting feed through five (5) cycles, and d) continuously of a program of movement of rapid traverse and cutting feed through ten (10) cycles. Ninthly, measurement of machine 0-point position accuracy and measurement of X-axis 10 mm-pitch position accuracy due to the laser measuring system were executed. Tenthly, the workpiece reference position was measured for axes X, Y and Z. Eleventhly, the electric power source was turned off. Twelfthly, the above-described steps 2.about.11 were executed repeatedly. PA1 (6) The simulated running conditions were such that a workpiece illustrated in FIG. 22 was assumed, and the aforesaid simulated running a) and b) were such that only movement of the X-axis was programmed, other axis movement was not practiced. Also, a program was prepared by dwell timing in place of the axis movement and movement energy of only the X-axis was the same as that of actual running. In short an attempt was made so as not to be influenced from axes other than the X-axis. The simulated running of the aforesaid c) and e) was such that 100 mm of rapid traverse and 50 mm (F200 mm/min) of cutting feed were repeated three times, and idle running was made without mounting of a workpiece with the above repeating serving as a program. Processing was estimated such that an upper surface was rough-processed with five (5) divisions and was finish-milled, was 6-12 drilled, was 7-8.2 drilled, and was 7-10 screw-drilled (tapped). PA1 (1) A change or variation of the workpiece reference positions, that is, the X, Y and Z positions due to simulated running according to conditions a) and b) above, and the X-axis machine 0-point position accuracy is as illustrated in FIGS. 26 and 27. According to FIGS. 26 and 27, first, fluctuation of the workpiece reference position at running of only the X-axis is not limited to the X-axis, but fluctuates together with Y and Z. Secondly, if running is done continuously at a constant cycle, the workpiece reference position is stabilized or becomes stable. If, however, the machine is halted, the workpiece reference position is fluctuated sensitively. Thirdly, the change of the X-axis machine 0-point accuracy changes together with running, but gradually becomes stable with running time. It will be understood that a maximum value is about 7 .mu.m. PA1 (2) A change of a position for each moving point due to the results of the simulated running in according to conditions c) and d) is as illustrated FIGS. 28.about.31. According to FIGS. 28.about.31, it will be seen that, first, the position of each part of the X-axis is sensitively fluctuated with movement running of the X-axis; secondly, a change in position of the X-axis is restored at the considerable rate or ratio to the initial or early condition by halt of the simulated running, and the restoring differs due to intervals of the halt period or duration; thirdly, positional accuracy of X+200. mm is fluctuated unsteadily even at the continuous running of a constant cycle; and fourthly, the positional accuracy of X-250. mm becomes substantially stable at continuous running of a constant cycle. PA1 possessing a plurality of thermal-displacement data, a thermal-displacement sampling time and a processing cycle time in memory means; PA1 causing a measurement reference position to serve as a machine origin; PA1 possessing data of the machine origin within the memory means; PA1 dividing an interior of the memory means such that input of a correction parameter can be executed with respect to the memory means in order to execute zero-point correction of measuring means; PA1 measuring shift of an absolute position of a machine origin as a measurement reference position before every processing, so that the shift of the absolute position serves as an initial value; PA1 turning of an electric power source; PA1 simultaneously executing collection of data of an amount of generated heat of thermal displacement of a ball screw and counting of a thermal-displacement sampling time; PA1 counting up the thermal-displacement sampling time; PA1 simultaneously executing adaptation processing which fluctuates the sampling time of the thermal displacement of the ball screw, depending upon whether or not the thermal displacement of the ball screw is within a range of an permissible error within processing cycle time, and comparison operation processing of the amount of thermal displacement; PA1 executing correction of the thermal displacement of the ball screw such that the error of the thermal displacement and a minimum movement setting unit are compared with each other to execute good or bad judgment of the processing; PA1 preparing interruption of correction of the thermal displacement of the ball screw, including promise items of breaks in a processing program of processing locations or processing groups during processing; PA1 always executing the interruption of correction of the thermal displacement of the ball screw at time other than the breaks or during running other than automatic running; and PA1 rewriting the plurality of thermal-displacement data to this-time data after correction of the thermal displacement, to execute thermal-displacement correction including processing of correction of the thermal displacement of the ball screw. PA1 initializing automatic correction after measurement of the machine origin; PA1 counting the measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing adaptation processing which fluctuates the measurement sampling time of the machine position and the moving position depending upon a fact that operation processing of the displacement of the machine origin and the thermal displacement are within the permissible error within the processing cycle time; PA1 executing the adaptation processing of the measurement sampling time of the machine position and the moving position so as to be repeated until an electric power source is turned off, regardless of a main processing; PA1 executing the correction of the machine origin such that the error and an permissible error value per time are compared with each other to decide whether or not the machine origin is required to be measured and corrected; PA1 executing prediction of the displacement of the machine origin on the basis of the following equation: EQU MotTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 comparing a prediction value of the displacement of the machine origin until the entire processing is completed and the permissible error with each other; PA1 executing warning during the automatic operation, automatic judgment on interruption of machine halt, and the machine halt on the basis of the results in which the prediction value of the displacement of the machine origin and the permissible error are compared with each other; PA1 after the machine halt is executed automatically, judging processing continuation by an operator; PA1 preparing the interruption of the machine halt, including promise items of breaks in the processing program of the processing locations and the processing groups during processing; PA1 always executing the interruption of the machine halt at time other than the breaks or during running other than automatic running; and PA1 executing the thermal-displacement correction including processing in which prediction, warning, measurement and correction are executed with respect to the displacement of the machine origin. PA1 executing the measurement and correction of the machine origin every time interval sampling; PA1 executing automatic judgment on the measurement interruption, the machine halt, and the displacement measurement and correction of the machine origin on the basis of results in which the prediction of the displacement of the machine origin is executed; PA1 measuring shift of the absolute position of the machine origin every measurement sampling time of the machine position and the moving position; PA1 reading this shift; and PA1 executing the thermal-displacement correction including correction processing of the machine origin from a subsequent machine operation. PA1 causing a measurement reference position to serve as a workpiece reference position; PA1 possessing at least data of a machine origin and a workpiece reference position in memory means; PA1 dividing an interior of the memory means so that input of a correction parameter can be executed with respect to the memory means in order to execute zero-point correction of measuring means; PA1 always measuring the workpiece reference position when an electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement serving as an initial value, to measure shift of an absolute position of the workpiece reference position every processing; PA1 reading the shift; and PA1 executing correction of thermal displacement including correction processing of the workpiece reference position, from a subsequent machine operation. PA1 possessing a plurality of thermal-displacement data, a thermal-displacement sampling time and a processing cycle time in the memory means; PA1 simultaneously executing, together with turning-on of an electric power source, collection of an amount of generated heat of thermal displacement of a ball screw and counting of sampling time of thermal displacement; PA1 counting up the sampling time of the thermal displacement; PA1 simultaneously executing adaptation processing in which the thermal-displacement sampling time of the ball screw is fluctuated, depending upon a fact that the thermal displacement of the ball screw is within a range of an permissible error within processing cycle time, and comparison operation processing of the amount of thermal displacement; PA1 executing correction of the thermal displacement of the ball screw such that the thermal displacement error and a minimum movement setting unit are compared with each other to perform good or bad judgment of the processing; PA1 preparing correction interruption of the thermal displacement of the ball screw, including promise items of breaks in a processing program of processing locations and processing groups during processing; PA1 always executing the interruption of correction of the thermal displacement of the ball screw at time other than the breaks or during running other than automatic running; and PA1 rewriting the plurality of thermal-displacement data to this-time data after correction of the thermal displacement, to execute thermal-displacement correction including correction processing of the thermal displacement of the ball screw. PA1 possessing measurement sampling time of an permissible value of a position error, a machine position and a moving position in memory means; PA1 initializing automatic correction after measurement of a workpiece reference position; PA1 counting measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing adaptation processing which fluctuates the measurement sampling time of the machine position and the moving position, depending upon a fact that operation processing of the displacement of the workpiece reference position and the thermal displacement are within the permissible error within the processing cycle time; PA1 executing the adaptation processing of the measurement sampling time of the machine position and the moving position so as to be repeated until an electric power source is turned off, regardless of a main processing; PA1 executing the correction of the workpiece reference position such that the error and an permissible error value per time are compared with each other to decide whether or not the machine origin is required to be measured and corrected; PA1 executing prediction of the displacement of the workpiece reference position on the basis of the following equation: EQU MwtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p 56 .multidot.k{Tc-(processing running time until now)}.sup.p PA1 where parameter "p" as used in this and other equations throughout this disclosure is a power factor having a value in the range of 0.5 to 10.0 and preferably 0.8 to 5.0, and is a measure of heat generation over heat emission PA1 comparing a prediction value of the displacement of the workpiece reference position until the entire processing is completed and the permissible error with each other; PA1 executing warning during the automatic operation, automatic judgment on interruption of machine halt, and the machine halt on the basis of the results in which the prediction value of the displacement of the workpiece reference position and the permissible error are compared with each other; PA1 after the machine halt is executed automatically, judging processing continuation by an operator; PA1 preparing the interruption of the machine halt, including promise items of breaks in the processing program of the processing locations and the processing groups during processing; PA1 always executing the interruption of the machine halt at time other than the breaks or during running other than automatic running; and PA1 executing the thermal-displacement correction including processing in which prediction, warning, measurement and correction are executed with respect to the displacement of the workpiece reference position. PA1 executing the measurement and correction of the workpiece reference position every time interval sampling; PA1 executing automatic judgment on the measurement interruption, the machine halt, and the displacement measurement and correction of the workpiece reference position on the basis of results in which the prediction of the displacement of the workpiece reference position is executed; PA1 measuring shift of the absolute position of the workpiece reference position every measurement sampling time of the machine position and the moving position; PA1 reading this shift; and PA1 executing the thermal-displacement correction including correction and processing of the workpiece reference position from a subsequent machine operation. PA1 causing a measurement reference position to serve as a workpiece-mounting reference-block position; PA1 possessing at least data of a machine origin and a workpiece-mounting reference-block position in memory means; PA1 dividing an interior of the memory means so that input of a correction parameter can be executed with respect to the memory means in order to execute zero-point correction of measuring means; PA1 executing measurement of the workpiece-mounting reference-block position when an electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement serving as an initial value; PA1 measuring shift of an absolute position of the workpiece-mounting reference-block position before every processing: PA1 possessing a plurality of thermal-displacement data, a thermal-displacement sampling time and a processing cycle time in memory means; PA1 simultaneously executing, together with turning-on of an electric power source, collection of an amount of generated heat of thermal displacement of a ball screw and counting of sampling time of thermal displacement; PA1 rewriting the thermal displacement data to this-time data after correction of the thermal displacement; PA1 counting up the sampling time of the thermal displacement; PA1 simultaneously executing adaptation processing in which the thermal-displacement sampling time of the ball screw is fluctuated, depending upon a fact that the thermal displacement of the ball screw is within a range of an permissible error within processing cycle time, and comparison operation processing of a thermal displacement error; PA1 executing correction of the thermal displacement of the ball screw such that the thermal displacement error and a minimum movement setting unit are compared with each other to perform good or bad judgment of the processing; PA1 preparing interruption of correction of the thermal displacement of the ball screw, including promise items of breaks in a processing program of processing locations and processing groups during processing; PA1 always executing the interruption of correction of the thermal displacement of the ball screw at time other than the breaks or during running other than automatic running; and PA1 rewriting the plurality of thermal-displacement data to this-time data after correction of the thermal displacement, to execute thermal-displacement correction including processing of correction of the thermal displacement of the ball screw. PA1 possessing measurement sampling time of an permissible value of a position error, a machine position and a moving position in memory means; PA1 after measurement of the workpiece-mounting reference-block position, initializing automatic correction; PA1 counting measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing adaptation processing which fluctuates the measurement sampling time of the machine position and the moving position, depending upon a fact that operation processing of the displacement of the workpiece-mounting reference-block position and the thermal displacement are within the permissible error within the processing cycle time; PA1 executing the adaptation processing of the measurement sampling time of the machine position and the moving position so as to be repeated until an electric power source is turned off, regardless of a main processing; PA1 executing no correction of the workpiece-mounting reference-block position in the case where the error is smaller than an permissible error value per time; PA1 executing correction of the workpiece-mounting reference-block position such that the error and the permissible error value per time are compared with each other to decide whether or not the workpiece-mounting reference-block position is required to be measured and corrected; PA1 executing prediction of the displacement of the workpiece-mounting reference-block position on the basis of the following equation: EQU MwbtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p 56 .multidot.k{Tc-(processing running time until now)}.sup.p PA1 comparing a prediction value of the displacement of the workpiece-mounting reference-block position until the entire processing is completed and the permissible error with each other; PA1 executing warning during the automatic operation, automatic judgment on interruption of machine halt, and the machine halt on the basis of the results in which the prediction value of the displacement of the workpiece-mounting reference-block position is compared; PA1 after the machine halt is executed automatically, judging processing continuation by an operator; PA1 preparing the interruption of the machine halt, including promise items of breaks in the processing program of the processing locations and the processing groups during processing; PA1 always executing the interruption of the machine halt at time other than the breaks or during running other than the automatic running; and PA1 executing the thermal-displacement correction including processing in which prediction, warning, measurement and correction are executed with respect to the displacement of the workpiece-mounting reference-block position. PA1 executing the measurement and correction of the workpiece-mounting reference-block position every time interval sampling; PA1 executing automatic judgment on the measurement interruption, the machine halt, and the displacement measurement and correction of the workpiece-mounting reference-block position, on the basis of results in which the prediction of the displacement of the workpiece-mounting reference-block position is executed; PA1 measuring shift of the absolute position of the workpiece-mounting reference-block position every measurement sampling time of the machine position and the moving position; PA1 reading the shift; and PA1 executing the thermal-displacement correction including correction and processing of the workpiece-mounting reference-block position, from a subsequent machine operation. PA1 possessing a machine origin, a specific moving position, an permissible value of position errors, each of a plurality of thermal-displacement data, a plurality of sampling time data, and processing cycle time, in memory means; PA1 simultaneously executing, together with turning-on of an electric power source, collection of an amount of generated heat of thermal displacement of a ball screw and counting of sampling time of thermal displacement; PA1 necessarily measuring the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position), when the electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement serving as an initial value; PA1 counting up the sampling time of the thermal displacement; PA1 executing adaptation processing in which the thermal-displacement sampling time of the ball screw is fluctuated, depending upon a fact that the thermal displacement is within a range of an permissible error within processing cycle time; PA1 after measurement of the machine position (for example, the machine origin, the workpiece reference position and the workpiece-mounting reference-block position, which is used as a reference position), initializing the automatic correction; PA1 executing counting of the measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing adaptation processing of measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing operation processing of the displacement of the moving position; PA1 executing the correction of the displacement of the moving position such that the error and the permissible error value per time are compared with each other; PA1 deciding whether or not measurement and correction of the moving position are required; PA1 executing predication of displacement of the moving position on the basis of the following equation: EQU MmtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p 56 .multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing judgment regarding the inside or the outside of the permissible value, such that the predication value of the displacement of the moving position and the permissible value are compared with each other; PA1 executing no correction in the case where the permissible value is not exceeded; PA1 executing warning during the automatic operation, automatic judgment on interruption of the measurement, and measurement and correction of the displacement of the moving position, on the basis of the results in which the prediction of the displacement of the moving position is executed; PA1 using, as the moving-position measurement, any one of or using in combination a reference-block three-fixed-point method, a constant deciding method due to actually measured data and a machine-outside measuring method; PA1 after correction of the thermal displacement, rewriting the plurality of thermal displacement data to this-time data; PA1 measuring shift of the absolute position of the moving position at each measurement sampling time of the machine position and the moving position; PA1 alternatively, computing a correction value of the moving position by the constant deciding method; PA1 reading the operated correction value; and PA1 executing correction of the thermal displacement, including correction processing of the moving position from a subsequent machine operation. PA1 counting up the sampling time of the thermal displacement; PA1 simultaneously executing adaptation processing which fluctuates the sampling time of the thermal displacement of the ball screw, depending upon a fact that the thermal displacement of the ball screw is within a range of the permissible error within the processing cycle time, and the comparative operation processing of the amount of thermal displacement; PA1 processing the collection of the data of the amount of generated heat of the thermal displacement of the ball screw, start of the counting of the thermal-displacement of sampling time and adaptation processing of the sampling time of the thermal displacement of the ball screw so as to be repeated until the electric power source is turned off, regardless the main processing; PA1 executing the correction of the thermal displacement of the ball screw such that the thermal-displacement error and the minimum movement setting unit are compared with each other to decide good or bad judgment of the processing; PA1 preparing the interruption of the correction of the thermal displacement of the ball screw, including promise items of breaks in the processing program of the processing locations and the processing groups during processing; and PA1 always executing correction of the thermal displacement at time other than the breaks or during running other than automatic running to execute correction of the thermal displacement including correction processing of the thermal displacement of the ball screw. PA1 possessing a machine origin, a workpiece reference position, a workpiece-mounting reference block position, and a plurality of thermal displacement data, in memory means; PA1 dividing an interior of the memory means so that input of a correction parameter can be executed with respect to the memory means in order to execute zero-point correction of measuring means; PA1 necessarily measuring the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position) when the electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement serving as an initial value; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing the displacement correction processing of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position) and the correction processing of the displacement of the moving position, in parallel relation to each other; PA1 promising the measurement processing with the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position) having a priority; PA1 executing the correction of the machine origin such that, in the case where the error is smaller than the error permissible value per time, no correction is made; PA1 executing prediction of the displacement of the machine origin on the basis of the following equation: EQU MotTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing prediction of the displacement of the workpiece reference position on the basis of the following equation: EQU MwtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing prediction of the workpiece-mounting reference-block position on the basis of the following equation: EQU MwbtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing warning during the automatic operation, automatic judgment on interruption of machine halt, the machine halt, and measurement and correction of the displacement of the machine origin, on the basis of the results in which the prediction of the displacement of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position) is executed; PA1 judging processing continuation by an operator, after the machine halt is automatically executed on the basis of the results in which the prediction of the displacement of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position); PA1 after correction of the thermal displacement, rewriting the plurality of thermal displacement data to this-time data; PA1 using means corresponding to each of the machine positions to measure shift of the absolute position of the machine position (the machine origin, the workpiece reference position and the workpiece-mounting reference-block position) before every processing; PA1 reading the shift; and PA1 executing correction of the thermal displacement, including correction processing of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position), from a subsequent machine operation. PA1 possessing a machine origin, a specific moving position, an permissible value of position errors, a plurality of thermal displacement data, a plurality of sampling time data, and a processing cycle time, in memory means; PA1 turning on an electric power source; PA1 simultaneously executing collection of data of generated heat of the thermal displacement of a ball screw and counting of sampling time of thermal displacement; PA1 counting up the sampling time of the thermal displacement; PA1 executing adaptation processing which fluctuates the sampling time of the thermal displacement of the ball screw, depending upon a fact that the thermal displacement is within a range of the permissible error within the processing cycle time; PA1 necessarily measuring the machine position when the electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement value serving as an initial value; PA1 initializing automatic correction after measurement of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position); PA1 executing counting of the measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing adaptation processing of the measurement sampling time of the machine position and the moving position; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing operation processing of the displacement of the moving position; PA1 executing the correction of the moving position such that the error and the permissible error value per time are compared with each other, to decide whether or not the measurement and correction of the moving position are required; PA1 executing prediction of the displacement of the moving position on the basis of the following equation: EQU MmtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing judgment on the inside and outside of the permissible value such that the prediction value of the displacement of the moving position and the permissible value are compared with each other; PA1 executing no correction in the case where the prediction value does not exceed the permissible value; PA1 executing warning during the automatic operation, automatic judgment on measuring interruption, and measurement and correction of the displacement of the moving position, on the basis of the results in which the prediction of the displacement of the moving position is executed; PA1 using, as the moving-position measurement, any one of or using in combination a reference-block three-fixed-point method, a constant deciding method due to actually measured data and a machine-outside measuring method; PA1 judging processing continuation by an operator, after the machine halt is automatically executed on the basis of the prediction of the displacement of the moving position; PA1 after correction of the thermal displacement, rewriting the plurality of thermal displacement data to this-time data; PA1 computing the moving position or computing a correction value of the moving position by the constant deciding method, every processing, to correct the measured or operated moving position; and PA1 executing correction of the thermal displacement including prediction, warning, measurement, correction and the like of the displacement of the moving position PA1 counting up the sampling time of the thermal displacement; PA1 processing the collection of the data of the amount of generated heat of the thermal displacement of the ball screw, the counting of the thermal-displacement sampling time, and the adaptation processing of the sampling time of the thermal displacement of the ball screw so as to be repeated until the electric power source is turned off, regardless the main processing; PA1 executing the correction of the thermal displacement of the ball screw such that the thermal-displacement error and the minimum movement setting unit are compared with each other to decide good or bad judgment of the processing; PA1 preparing the interruption of the correction of the thermal displacement of the ball screw, including promise items of breaks in the processing program of the processing locations and the processing groups during processing; PA1 always executing the interruption of the correction of the thermal displacement at time other than the breaks or during running other than the automatic running; and PA1 executing correction of the thermal displacement, including processing of correction of the thermal displacement of the ball screw. PA1 possessing a machine origin, a workpiece reference position, a workpiece-mounting reference-block position, a plurality of thermal displacement data, and the like, in memory means; PA1 dividing an interior of the memory means so that input of a correction parameter can be executed with respect to the memory means in order to execute zero-point correction of measuring means; PA1 necessarily measuring the machine position when the electric power source is turned on; PA1 bringing correction values entirely to zero with a value of the measurement serving as an initial value; PA1 counting up the measurement sampling time of the machine position and the moving position; PA1 executing the correction processing of the displacement of the moving position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position) and the correction processing of the displacement of the moving position, in parallel relation to each other; PA1 promising the measurement processing with the measurement of the machine position (the machine origin, the workpiece reference position, the workpiece-mounting reference-block position) having a priority; PA1 executing the correction of the displacement of the machine position such that the error and the error permissible value per time are compared with each other to decide whether or not measurement and correction are required; PA1 executing prediction of the displacement of the machine origin on the basis of the following equation: EQU MotTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing prediction of the displacement of the workpiece reference position on the basis of the following equation: EQU MwtTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing prediction of the workpiece-mounting reference-block position on the basis of the following equation: EQU MwbTcf.varies.{.vertline.(previous time)-(this time).vertline./(Tp).sup.p }.multidot.k{Tc-(processing running time until now)}.sup.p PA1 executing warning during the automatic running, automatic judgment on interruption of machine halt, the machine halt, and measurement and correction of the displacement of the machine origin, on the basis of the results in which the prediction of the displacement of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position); PA1 judging processing continuation by an operator, after the machine halt is automatically executed on the basis of the results in which the prediction of the displacement of the machine position (the machine origin, the workpiece reference position, and the workpiece-mounting reference-block position); PA1 after correction of the thermal displacement, rewriting the plurality of thermal displacement data to this-time data; PA1 measuring shift of the absolute position of the machine position (the machine origin, the workpiece reference position and the workpiece-mounting reference-block position) before every processing; PA1 reading the shift; and PA1 executing correction of the thermal displacement, including correction processing of the machine position from a subsequent machine operation. PA1 judging reprocessing after measurement and correction depending upon presence of a finish margin; PA1 bringing the reprocessing to alarm processing with n times of loops waited; and PA1 executing correction of the thermal displacement including processing in which position displacement is predicted, warned, measured, corrected and the like. The method of thermal-displacement correction according to the eighteenth embodiment enables reprocessing after measurement correction.
B. Results:
II. Operation No. 2
Another conventional measuring method will next be described below.
A. Measuring Method:
B. Results:
As appearing from the data of the above-described experimental results which do not include cutting processing, in order to compensate or correct the machine position and the moving position which vary with time, i.e. hourly, use of only the simple methods proposed until now cannot provide the necessary correction of the positional fluctuation the entire machine. Further, it is impossible for the simple method to execute automatic correction under the control of an operator.
The conventional correction of thermal displacement is directed to a method in which generated heat is removed, as described previously, so that an objective temperature is approached as closely as possible. Alternatively, the conventional correction uses a method in which generated heat due to integrated power which causes thermal displacement is compensated by multiple position corrections. Since the conventional correction techniques do not compensate for compounded thermal displacement, the conventional correction has several problems. First, the accuracy of correction of the thermal displacement is low. Moreover, the former case necessitates a cooling device and structures, making the apparatus cost high.
In view of the aforesaid experimental results, it has been desired to apply the numerical control apparatus to a system which can cope with the above problems, in order to accurately or exactly grasp the accuracy of the machine position and the moving position which vary over time, to execute feed-back correction, and thereby to provide machining at high accuracy.